Thermal trip mechanism for circuit breakers



R. KERN 2,

THERMAL TRIP MECHAKISM FOR CIRCUIT BREAKERS Feb. 24, 1953 Filed June 18,1949 Fig.1.

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F IR 8 H Patented Feb. 24, 1953 THERMAL TRIP MECHANISM FOR CIRCUITBREAKERS Ruth Kern. Drexel Hill, Pa., assignor to General ElectricCompany, a corporation of New York- Application June 18, 1949, SerialNo. 100,025

3 Claims. 1

This invention relates to trip units for. circuit breakers and inparticular to devices that automatically trip to the open position thecontacts of a circuit breaker at predetermined overload currents.

Circuit breakers of the subject class are placed directly in electricallines and serve the function of interrupting the passage of currentthrough the lines when, due to some variation or imperfection in theload circuit, a current equal to or greater than that at which thecircuit breaker trip unit is calibrated passes through the lines.

Circuit breakers of the subject type have various operating principles,but one of the more simple types is to have a bimetallic unit operate atripping mechanism-with an inverse time delay when the bimetallicelement is heated by load current greater than that at which the circuitbreaker trip unit is calibrated to trip with maximum time delay.

Thus the present invention deals primarily with a bimetallic inversetime delay tripping unit that is used to trip to the open position thecontacts of a circuit breaker.

An object of this invention is to provide an improved removable singleplug. contact mounted juxtaposed bimetal trip unit structure capable ofcalibration at different current ratings to enable interchangingbimetallic units in acircuit breaker so that the circuit breakermay'have a rated current ranging from to 200 amperes.

A further object of this invention is to facilitate the production ofcircuit breakers with the resultant benefits in the art by providing ameans whereby one construction of circuit'breaker operates on a Widerange of rated currents.

A still further object of-this invention is to provide a simple methodof interchanging.bimetallic units within a circuit breaker.

A still further object is to'provide a bimetallic un-itfor circuitbreakers'which requires minimum operative space.

In its broadest form, this invention comprises a bimetallic means fortripping a circuit breaker at overload current. The said bimetallicmeans is readily'interchangeable allowing the same circui-t' breakerto-be used for various currents up to 200 amperes.

Further. objects and advantages of this invention will become apparent,"and the invention will be better understood from" the followingdescription referring to the accompanying drawing, and the features ofnovelty which characterize this invention will be pointed outwithparticularity in the claims annexed to and forming a part of, thisspecification.

In the drawing, Fig. 1. is a front elevation, partially in section, of acircuit breaker embodying my invention.

Figs. 2, 3 and 4 are perspective views of modifications of thebimetallic unit used in the circuit breaker of Fig. 1.

In the circuit breaker l of Fig. 1, an electrical path is provided thatcomprises a mounting stud 2 which serves to removably mount andelectrically connect both the circuit breaker and the trip unit and islocated at the point where line current enters the circuit breaker,suitable securing nuts 3, a clip terminal 4, a matching prong or plugcontact 5, stud B, bimetallic unit I, .pigtall 8, movable arm 9, movablecontact I0, fixed contact ll, mounting stud l2 which is connected to anelectric load, and corresponding nut l3.

Line current is brought into .the circuit breaker through stud 2by meansof a lead (not shown) which is held in contactwith stud 2 by means ofnuts 3. The current passes through stud 2, which is embedded in aplastic base I 4, to clip terminal 4 connected to stud 2. The currentpasses from clip terminal 4 to matching prong 5 and through stud 6,which is an integral part of the bimetallic unit I, tov pigtail 8 weldedto bimetallic unit I, through movable arm 9 tocontact l0 which isrigidly recured' to the movable arm 9. The current passes from contactH] to fixed contact ll, to stud l2 and from stud 12 to an electric load(not shown) which is attached to stud l2 by means of a lead (not shown)held in place by nut l3.

The plastic base M is removably secured to the body portion I5 of thecircuit breaker allowing the bod portion to be removed from the base andprong 5 to be removed from clip terminal 4. When the body portion [5 hasbeen removed from the base plate I4, and the cover [5 from body portionIS, the bimetallic unit 1 is readily accessible.

The bimetallic unit comprises prong 5, stud 6; which is held in contactwith the body portion 15 of circuit breaker I by means of nut IS, amounting .plate 11, a bimetallic element 18, resistor I 9, seriesresistorZO, shunt resistor 2 l magnet 22, terminal plate 23 for pigtail8 which is electrically connected with the movable contact arm 53carrying contact [0.

Prong 5, an integral part or stud 6, is arranged opera-tively to engagethe spring terminal 4. The contour of prong '5 is such that it may beremovably secured within spring contact 4 giving secure electricalcontact that allow-spassage of current from stud 2 to stud 6. Stud 6 isri idly fastened to mounting plate H, and is the secur- 3 ing means forfastening the bimetallic unit 1 to the body portion I5 of the circuitbreaker. Stud 6 is inserted through an opening 24 in the body portion ofthe circuit breaker and held in place by nut I6 which engages a shoulderin the body portion I5.

At point 26, one end of the bimetallic element I8 and one leg ofresistor I9 are welded to the mounting plate I! as indicated in Fig. 2of the drawing. Current flows from stud 6 through mounting plate H topoint 26 where it divides. part going through bimetallic element I8 andpart going through resistor I9. The current paths are joined again atpoint 21 Where leg 29 of resistor I9 and bimetallic element 29 join thesupport plate 23 as shown in Fig. 2.

The bimetallic elements I8 and 29 each comprise two strips of metalhaving different ccefiicients of expansion. Thus, the outer stri 39 ofelement I8 has a higher coefiicient of expansion than the inner strip3|. The two strips are duplicates and rigidly secured together, inparallel juxtaposition and when heated the top of the bimetallic elementbends toward a pin 32 (shown in Fig. 1) which operates a trippingmechanism (not shown) The two bimetallic elements l8 and 29 are joinedby a series resistor 29and a shunt resistor 2|. In this construction,shunt resistor 2| functions as a calibrating bar. That is, the currentcarrying capacity or rating of the bimetallic unit can be changed byvarying the position of the shunt resistor 2| alon the length of thebimetallic elements I8 and 29. The further shunt resistor 2I ispositioned from series resistor 20, the greater is the current rating ofthe particular bimetallic unit.

Resistor I9 is of substantially uniform cross section and U-shaped, andby changing the size of its cross section, the rating of the bime allicunit can bevaried. From points 26. 21 the resistor is bent away frombimetallic elements I8 and 29, and then at points 26a it is bent againto. run parallel to them. Heat generated in the resistor I9 by currentpassing therethrough is radiated to the bimetallic elements uniformlysince both legs of the resistor are of equal size andthe heat aids inthe bending of the bimetallic elements.

An electromagnet 22 in the form of a U-shaped ferromagnetic memberfunctions as an emergencytrip and is securely mounted on bimetallicelement I8. When very high current passes through the circuit, such asthat caused by a short circuit, a magnetic force is set up in themagnetby the passage of current through bimetallic element I8, toattract an armature 33 which is operatively associated with the pin 32to cause a tripping mechanism (not shown) to function and open contactI0 away from fixed contact II. By employing the magnet 22, the contactsof the circuit breaker can be caused to open by the pull of the magneton arm 33 before the high current has an opportunity to fuse theelements of the bimetallic unit. The magnet 22 is so designed that itdoes not function at rated or slightly above rated current, but doesfunction only at current levels of the order of short circuit.

Support member 23 preferably comprises a U- shaped portion 36 that formsa mounting seat in off et alignment with the axis of the terminal plug 6for removablyanchoring the bimetal e ement 29 of unit I in position onthe bod portion I501 th circuit breaker 'I, a flat portion 31 and anupbended portion 38;. Current after leaving bimetallic element 29 andleg 28 of resistor I9 passes through the U-shaped portion 36 of supportmember 23 to pigtail 8 and from pigtail 8 to movable arm 9 that supportscontact ID. The flat portion 31 with its offset upbent arm 38 serves thefunction of protecting the support plate H from the pigtail. That is, itis arranged to prevent electrical contact between support plate I! andpigtail B, and the upbent arm 36 acts as a shield between the freeportion of the pigtail and the mounting plate II.

Movable contact arm 9 is electrically connected to pi tail 8 by brazing,and, is an integral part of the bimetallic unit; consequently, when abimetallic unit is installed, a corresponding movable contact arm 9 isalso installed. The contact arm 9 is mounted on suitable studs 34 and 35which in turn are associated with the tripping mechanism (not shown) andwhich cause the outer end of contact arm 9 which carries contact I0either to be brought in touch with or away from fixed contact I I.

In operation, current enters from a supply line to stud 2 through cliterminal 4 to matching prong 5, through stud Gto mounting plate I'I intobimetallic unit I through support member 23, pigtail 8 and movable arm 9to contact I 0. When contact I0 is closed on contact II, current passesthrough contact I I to stud I2 to the electrical load.

Load current passing through resistor I9 and bimetallic unit I heats theelements I8 and 29, causing them to deflect, and resistor 20 approachespin 32. The unit is constructed so that, when current at a certainpercentage greater than rated passes through the bimetallic unit, enoughheat is generated to cause resistor 20 to pu h against pin 32 andthereby operate a tripping mechanism that causes movable contact arm 9and its associa ed contact I0 to move away from fixed contact II It isto be understood that suitable arc quenching means are also employed todestroy the are that extends from contact I 0 to contact lI uponopening,

If a very high current, such as that caused b short circuit, passesthrough bimetallic unit I, magnet 22 is energized attracting arm 33which is operatively associated with pin 32 and causes the trippingmechanism to function and open the contacts. I 0 and I I. By use of manet 22, the high short circuit current is interrupted before it hasopportunity to'fuse the component parts of the bimetallic unit.

When it is desired to change the rating of one of the subject typecircuit breakers, the body portion 15. of the circuit breaker is removedfrom the base portion I4 simply by pulling contact plug 5 out of socket4. When the cover portion I5 has been removed from body portion I5, thebimetallic unit is then readily accessible and nut I6 may be removedfrom stud 6 allowing the bimetallic unit to be withdrawn from the bodyportion I5 after movable contact arm 9 has been removed from pins 34 and35. A new bimetallic unit of a different rating is then installed in thesame manner. That is, movable contact arm 9 is replaced on pins 34 and35 and stud 6 is inserted through opening 24 and fastened in place bynut I6. The body portion I5 of the circuit breaker is then replaced onthe base portion I4 of the circuit breaker with prong 5 coming intooperative engagement with spring clip 4. Nuts'36 arethen-fastenedto stud31 and the circuit breaker is again ready for operation a'ta differentcurrent rating;

Two other; types: or; bimetallic unitsewhichmre interchangeable:withtth'atshown ini Fig.2 L and Fig. 2 are-illustratedintFi'gs. 3:and14?flthedraw ing. Bimetallic units!! shown: in; Fig: -3isr of the typethat" hasiarating ore-u; amperes; while bimetallic unit 40 shownln;Fig.4; theiatype that has a rating of amperes. Both bimetallic units 39.and operate the tripping. mechanism exactly as thebimetallic"unitishowrr in Figs: 1 and 2; Specifically, theKupperm'ost-bars 4| and42 of. bimetallic units" 39:" and. 40,: respectively, press againstbutton to trip the circuittbreal-b er. In addition; each' of thebimetallic units33 and 40 has a magnet 43 and.44, respectively, thatautomatically: trips the circuit in case ofi short circuit current;

Inv bimetallic unit 39;prong 5d, a stud ficiand a mounting'plate-|laiare provldediwhichare the duplicates. of: prongs: 5, 6 T and I Icomprising. part of bimetallic unit 1; rigidly securedfito mountingplate" l1a-- and is joined by a seriesreslstor "inatherform of" bar 4|to bimetallicelementiwhich is theduplicate of and which is located-inspaced alignment with bimetallic element 45. Ar -supporting plate--41 isrigidly secured tothe' bottom" of bimetallic element 46'. 'Thissupport-plated is similar to plate 23. used for bimetallic unit 1.Pigtail" 48 connects the support plate: 4-|' with armovable arm- (notshown) similar to' arm 9 shown-in Fig. 1-. The upturned: lip'= 48 ofsupport plate-41 serves the function: of. protecting plate Na" andbimetallic element from electrical contact with' pigtail- 49'.

When bimetallic unit 39 is used to replace bi metallic unit 1, currentpasses from spring" clip 4 into prong 5a through stud Sarto mountingplatel'la and from there into bimetallic element 45 across seriesresistorv 4|. and down bimetallic element 46 to support plate" '41through pigtail 49 and the" movable contact-armrtoithei'contact.

I0 of the breaker.

The bimetallic elements 45 and45- comprise a high expansion metal on theouter side and a low expansion metal on the inner side rigidly fastenedtogether, causing. bimetallic elements 45 and 46-tobendso that seriesresistor 4| ap proaches pin 32 when the bimetallic'el'ements are heatedby load current passing therethrough.

If the current passing throughthe bimetallic element is greater thanrated current, the element deflects to the extent that; series: resistor4| pushes against button 32 causing themechanism to trip open contactsHi0. and IL. If, on

the other hand, current of" the short circuit magnitude passesthroughthebimetallic element 45, a magnetic attractive force is inducedin magnet 43 that attracts'arm 33 of the tripping mechanism; causingcontacts Illa; and II to be opened. By changing the cross section andmaterial of the component parts of bimetallic unit 39, it can bedesignedto have a rated current of from 50 to 100 amperes.

Bimetallic unit 49, illustrated in Fig. 4 of the drawing, comprisesprong 5b, stud 5b, mount Bimetallic" element" 45 1s .ment 50 withbimetallic element 6 sulating strip: 42v to deflect toward button when:the bimetallic element is heated.

A. U-shaped resistor 52 joins bimetallic" ele- The U-shaped resistor 52comprises two legs 5| and '54 bent away from the two bimetallic elements'50'and' 55. Tnetwolegs 5| and 54 oi'the series resistor 52 in order toprotect it from electrical contact with magnet 44 and trip arm 33 whichis located near the U-shaped resistor.

shown in Fig. l.

A U-shaped magnet 4 is rigidly secured to bimetallic element 50. andserves the same function as 'magnets: 22' and 43 shown in Figs. 2 and 3,Specifically, it attracts tripping arm 33 when current of short circuitmagnitude passes through bimetallic element 59 causing movable contactarm. 91) to separate contacts I01) and H.

A support plate 55 is rigidly secured to the lowermost portion ofbimetallic element 55, and a pigtail-to conducts current fromsupport'plate 56. to amovable contact arm similar to arm 9 Support plate55 has an upturned portion 6| whichshields the series resistor 52 fromcontact with pigtail 60'. Aninsul'ating 'block 62 1s employed to preventthe upturned portion 6| ofmounting plate 55 from contacting crossbar 53of series resistor 5| and possibly in;

terfering with operation of tripping arm 33.

When a bimetallic unit of the type shown in Fig. 4 is inserted inoperative position within the 1 through support plate 55, pigtail Eli,to the movable arm and contact, through the movable contact to fixedcontact H, out stud IE to the electrical load.

Heat" generated in the. bimetallic elements 50; 55 and in the seriesresistor 52 causes the bimetallic elements 50 and 55 to deflect so thatinsulating bar 42' approaches pin 32. If greater than rated currentpasses through the bimetallic e1ements, the insulating bar 42 pressesagainst -'.pin 32, causing the mechanism to trip to the .open position.If current of short circuit magnitude passes through the bimetallic unit40, magnet 44 is activated and attracts arm 33 of the trippingmechanism, causing the circuit breaker to trip to the open position.

While different modifications of the bimetallic units are shown in Figs.2, 3 and 4, it is to be understood, however, that by varying thephysical size of the component parts of each of these bi- ,jmetallicunits, the current rating of each unit can be changed to handle a widerange of currents.

- Consequently, by interchanging the three units shown and by changingthe physical size of the component parts, it is possible to use onecircuit breaker of the type illustrated in Fig. 1 at any current ratingof from 10 to 200 amperes.

Modifications of this invention will occur to those skilled in the art,and it is desired to be understood, therefore, that this invention isnot to be limited to the particular arrangement enclosed, but that theappended claims are meant to cover all the modifications which do notdepart from the spirit and scope of this invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A circuit breaker trip unit having in combination a mounting plateprovided with a single projecting terminal plug contact having threadedmeans for removably mounting the plug and plate on the circuit breaker,a pair of duplicate bi-metallic elements carried by the mounting platein spaced apart parallel juxtaposition and having rigid resistor meansfor heating the ele- I ments and for mechanically interconnecting theelements in conducting relation with only one end of one element mountedupon and electrical-- 1y connected with the mounting plate, a tripmember carried by the free ends of the parallel bi-metallic elements, aflexible pigtail for connection with the circuit breaker and having aconducting terminal forming a mounting seat in offset alignment with theof the terminal plug contact and electrically and mechanically,connected with the other end of the parallel bimetallic element toeffect deflection of the free ends of the bi-metallic elements inresponse to the heating effect of the current passing from the pigtailthrough the bimetallic elements and the resistor means to the terminalplug contact and thereby effect operation of the trip member in thetripping direction. 2. A circuit breaker trip unit having in combinationa supporting plate provided with a single projecting terminal plugcontact having threaded means for removably securing the plug and plateon the circuit breaker, a first bi-metallic element secured at one endto the mounting plate, a second bi-metallic element supported in spacedparallel juxtaposition with the one bi-metallic element and having arigid series resistor mechanically and electrically interconnecting theother end of the one bi-metallic element with the adjacent end of thesecond bi-metallic element Number end of the second bi-metallic elementto effect deflection of the bi-metallic elements in response to theheating effect of the current flowing from the pigtail through theelements and the resistors to the terminal plug contact and therebyeffect operation of the trip member in the tripping direction.

3. A circuit breaker trip unit having in combination a mounting plateprovided with a single projecting terminal, a plug contact havingthreaded means for removably securing the plug and plate on the circuitbreaker, a pair of bimetallic elements supported by the mounting platein spaced apart parallel juxtaposition with onlyone end of one elementmounted upon and electrically connected with the mounting plate, aninsulatingbar joining the other end of the one bi-metallic element withthe adjacent end of the other bi-metallic element to form a trip member,a U-shaped series resistor having one end thereof electrically connectedwith the other end of one bi-metallic'-,.e lement and the'other endthereof with the adjacent end of the other bi-metallic element andextending in spaced apart parallel juxtaposition with the elements, aflexible pigtail having a terminal member forming amounting seat inoflset alignment with the axis of the terminal plug contact andmechanically and electrically connected with the other end of the otherbi-metallic element for effecting deflection of the bi-metallic elementsin responseto the heating effect of the current passing from-the pigtailthrough the elements in series with the U-shaped resisto'rito'theterminals and thereby effect-operation of the'trip member formed by theinsulating bar in the tripping direction. I

a --RUTH KERN.

REFEREN'CES CITED The following references are of record in the file ofthis patent:

' UNITED STATES PATENTS Name Date 1,622,907 Getchell Mar. 29, 19271,838,950 Lindstrom Dec. 29, 1931 2,013,011 Sheldon Sept, 3, 19352,015,598 r Langfritz Sept. 24, 1935 2,050,879 Erben Aug. 11, 19362,052,564 Grady Sept. 1, 1936 2,074,584 Graves, Jr. Mar. 23, 19372,180,421 Leonard Nov. 21, 1939 2,443,090 Wise June 8, 1948 2,447,652Jennings Aug. 24, 1948 FOREIGN PATENTS Number Country Date 427,512Great'Britain Apr. 12, 1935

